Method for Producing an Optoelectronic Semiconductor Device and Optoelectronic Semiconductor Device

ABSTRACT

A method for producing an optoelectronic semiconductor device and an optoelectronic semiconductor device are disclosed. In an embodiment the method includes providing a semiconductor layer sequence including a light-emitting and/or light-absorbing active zone and a top face downstream of the active zone in a stack direction extending perpendicular to a main plane of extension of the semiconductor layer sequence, applying a layer stack onto the top face, wherein the layer stack includes an oxide layer containing indium, and an intermediate face downstream of the top face in the stack direction and applying a contact layer onto the intermediate face, wherein the contact layer includes indium tin oxide, and wherein the layer stack is, within the bounds of manufacturing tolerances, free of tin.

This patent application is a national phase filing under section 371 ofPCT/EP2016/063891, filed Jun. 16, 2016, which claims the priority ofGerman patent application 10 2015 109 786.9, filed Jun. 18, 2015, eachof which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

U.S. Patent Application Publication No. 2011/0284893 A1 describes amethod for producing an optoelectronic semiconductor device and anoptoelectronic semiconductor device.

SUMMARY OF THE INVENTION

Embodiments of the invention provide a method for producing anoptoelectronic semiconductor device with improved electrical contacting.Further embodiments provide an optoelectronic semiconductor device withimproved electrical contacting.

The optoelectronic semiconductor device may be designed to emit and/orabsorb light during operation. The optoelectronic semiconductor deviceis, for example, a light-emitting diode, a photodiode and/or asemiconductor laser diode.

According to at least one embodiment of the method, a semiconductorlayer sequence is provided. The semiconductor layer sequence has a mainplane of extension in which it extends in lateral directions. A stackdirection of the semiconductor layer sequence extends perpendicular tothe main plane of extension. Along the stack direction, thesemiconductor layer sequence has a thickness which is small incomparison with the maximum extent of the semiconductor layer sequencein the lateral directions. A main plane of the semiconductor layersequence forms a top face of the semiconductor layer sequence.

The semiconductor layer sequence may be grown epitaxially, in particularby means of metal-organic vapor phase epitaxy (MOVPE), on a growthcarrier. It is here possible for the growth carrier to be removed againfrom the semiconductor layer sequence in a method step subsequent togrowth. The semiconductor layer sequence may contain a multiplicity ofsemiconductor layers which are arranged one above the other in the stackdirection. Each of the semiconductor layers may extend along the mainplane of extension. The semiconductor layers may be formed with asemiconductor material. In particular, the semiconductor layer sequencemay be based on a nitride compound semiconductor material.

“Based on nitride compound semiconductors” may here and hereinafter meanthat the semiconductor layer sequences or at least one semiconductorlayer thereof, preferably each semiconductor layer of the semiconductorlayer sequence, comprises a nitride-III/V compound semiconductormaterial, preferably Al_(y)In_(x)Ga_(1-x-y)N, wherein 0≤x≤1, 0≤y≤1 andx+y≤1. Here, this material does not necessarily have a mathematicallyexact composition according to the above formula. Instead, it mayinclude one or more dopants and additional constituents which do notsubstantially modify the characteristic physical properties of theAl_(y)In_(x)Ga_(1-x-y)N material. For simplicity's sake, however, theabove formula includes only the fundamental constituents of the crystallattice (Al, Ga, In, N), even if these may in part be replaced by smallquantities of further substances.

According to at least one embodiment of the method, the semiconductorlayer sequence comprises a light-emitting and/or light-absorbing activezone. The top face of the semiconductor layer sequence is downstream ofthe active zone in the stack direction. In particular, the active zoneemits or absorbs light in the visible and/or ultraviolet region of theelectromagnetic spectrum. The emitted light may have a wavelength, inparticular a peak wavelength, of at least 200 nm and at most 540 nm,preferably at least 400 nm and at most 500 nm and particularlypreferably at least 430 nm and at most 470 nm.

The semiconductor layer sequence, for example, comprises a firstsemiconductor layer, the active zone, a second semiconductor layer and ahighly doped semiconductor layer. The highly doped semiconductor layermay, for example, be p-doped. The active zone may be arranged betweenthe first and second semiconductor layers. The active zone may here, forexample, take the form of a layer or layer sequence and be formed with asemiconductor material. The highly doped semiconductor layer may bearranged on the second semiconductor layer in the stack direction. It isin particular possible for the second semiconductor layer and the highlydoped semiconductor layer to be in direct contact with one another andin particular to be electrically conductively connected to one another.An outer face of the highly doped semiconductor layer may form the topface.

The highly doped semiconductor layer may in particular be doped withmagnesium. The magnesium dopant concentration in the highly dopedsemiconductor layer may amount to at least 5*10¹⁹/cm³, preferably atleast 1.0*10²⁰/cm³ and particularly preferably at least 1.2*10²⁰/cm³,and at most 9*10²⁰/cm³, preferably at most 5*10²⁰/cm³ and particularlypreferably at most 2*10²⁰/cm³. The highly doped semiconductor layer may,for example, be activated with an oxygen-containing gas.

According to at least one embodiment of the method, a layer stack isapplied to the top face. The layer stack may, for example, be appliedonto the top face by means of epitaxial deposition and/or sputtering.The layer stack may have a plurality of layers which are arranged oneabove the other in the stack direction and may in each case extend alongthe main plane of extension.

The layer stack has an oxide layer which contains indium. In particular,the oxide layer may contain indium oxide, preferably In₂O₃, or, withinthe bounds of manufacturing tolerances, consist thereof. A layerconsisting of a material “within the bounds of manufacturing tolerances”here and hereinafter means that production-related impurities of afurther material may be present in said layer.

The layer stack furthermore comprises an intermediate face which isdownstream of the top face in the stack direction. The intermediate facemay be an outer face of the layer stack remote from the semiconductorlayer sequence. In particular, the intermediate face may be formed by anouter face of the oxide layer.

The layer stack and in particular the oxide layer may belight-transmitting. A layer or layer stack is here and hereinafter“light-transmitting” if said layer or layer stack has a transmissioncoefficient for the light emitted or absorbed by the active zone duringoperation of the optoelectronic semiconductor device of at least 80%,preferably at least 90% and particularly preferably at least 95%.

It is furthermore possible for the layer stack to be electricallyconductive. In particular, the layer stack may be electricallyconductively connected to the semiconductor layer sequence. For example,the layer stack is in direct electrical contact with the highly dopedsemiconductor layer.

According to at least one embodiment of the method, a contact layer isapplied onto the intermediate face. The contact layer is formed withindium tin oxide (ITO). In particular, the contact layer may, within thebounds of manufacturing tolerances, consist of indium tin oxide. Forexample, the contact layer is formed with In_(a)Sn_(1-a)O, with0.75≤a≤0.99, preferably a≤0.98.

The contact layer may in particular be applied using a plasma-freedeposition method, such as, for example, MOVPE. As a result, amonocrystalline contact layer may be obtained which may be free of grainboundaries. In contrast, it is possible for a contact layer, applied,for example, by means of sputtering, still to have grain boundaries.

The contact layer may be light-transmitting. For example, an outer faceof the contact layer remote from the layer stack may form a lightpassage face of the optoelectronic semiconductor device. Light may becoupled out from or injected into the optoelectronic semiconductordevice through the light passage face.

In particular, the contact layer is electrically conductive. The contactlayer may serve for electrically contacting the semiconductor layersequence. In particular, the contact layer may be electricallyconductively connected to the semiconductor layer sequence by means ofthe layer stack.

According to at least one embodiment of the method, the layer stack is,within the bounds of manufacturing tolerances, free of tin. A layer orlayer stack being, within the bounds of manufacturing tolerances, freeof an element and/or a material may here and hereinafter mean thatmerely traces of said element and/or material are present in the layeror layer stack as a result of production-related contaminants. Diffusionof the element and/or material from adjacent layers into the layer orthe layer stack should here likewise be considered to beproduction-related contamination. The layer stack thus contains, withinthe bounds of manufacturing tolerances, no tin, in particular no indiumtin oxide. In particular, the number of tin atoms in the layer stack mayamount to at most 1%, preferably at most 0.5% and particularlypreferably at most 0.1%, of the number of indium atoms in the layerstack or tin is not detectable in the layer stack.

According to at least one embodiment of the method for producing anoptoelectronic semiconductor device, the method comprises the followingsteps: providing a semiconductor layer sequence, including alight-emitting and/or light-absorbing active zone and a top facedownstream of the active zone in a stack direction extendingperpendicular to a main plane of extension of the semiconductor layersequence, applying a layer stack onto the top face, wherein the layerstack comprises an oxide layer, which contains indium, and anintermediate face downstream of the top face in the stack direction,applying a contact layer, which is formed with indium tin oxide, ontothe intermediate face, wherein the layer stack is, within the bounds ofmanufacturing tolerances, free of tin.

The method steps may be performed in the stated sequence.

In the method described here for producing an optoelectronicsemiconductor device, the intention is to avoid direct application ofthe contact layer onto the semiconductor layer sequence in order toimprove electrical contacting of the semiconductor layer sequence. Tothis end, the layer stack is arranged between the semiconductor layersequence and the contact layer. By means of the layer stack, the contactlayer can be prevented from directly adjoining the semiconductor layersequence and in particular the top face of the semiconductor layersequence may already be protected prior to deposition of the contactlayer.

In an alternative semiconductor device, in which the contact layer isapplied directly onto the top face of the semiconductor layer sequence,for example, by means of sputtering, and no layer stack is thus present,cracks, contaminants and/or defects may occur in the semiconductor layersequence and/or contact layer in an alternative boundary region betweenthe contact layer and the semiconductor layer sequence. As a result,electrical contact between the contact layer and the semiconductor layersequence may be impaired in the alternative semiconductor device andconsequently in particular the voltage drop at the alternative boundaryregion may be increased.

Introducing the layer stack may reduce the voltage drop at thesemiconductor device by up to 100 mV in comparison with the alternativesemiconductor device. It has here surprisingly been found that, due tothe layer stack, it is possible to improve material quality, forexample, the quality of the crystal structure and/or intactness, in afirst boundary region between the semiconductor layer sequence and thelayer stack and/or in a second boundary region between the layer stackand the contact layer. In particular the oxide layer which containsindium may here contribute to improving crystal quality and/or toprotecting the crystal structure of the top face of the semiconductorlayer sequence.

According to at least one embodiment of the method, a nitride layerwhich contains indium is firstly provided for application of the oxidelayer. The nitride layer may be provided by a growth method, such as,for example, MOVPE, molecular beam epitaxy (MBE) or sputtering.

The nitride layer may in particular be formed with or consist of indiumnitride, preferably InN. The nitride layer may be opaque. A layer ishere and hereinafter “opaque” if the layer has a transmissioncoefficient for the light emitted or absorbed by the active zone duringoperation of the optoelectronic semiconductor device of at most 60%,preferably at most 50% and particularly preferably at most 40%. Inparticular, an opaque layer may an energy band gap which is smaller inmagnitude than the energy of a photon of the light emitted and/orabsorbed by the active zone.

According to at least one embodiment of the method, the nitride layer isat least partially oxidized in an oxidation step to yield the oxidelayer. The oxidation step may take place in a method step subsequent todeposition of the nitride layer. The oxidation step may, for example, becarried out directly after deposition. It is alternatively oradditionally possible for the oxidation step to be carried out as earlyas during deposition.

For oxidation, an oxygen-containing gas may be admitted into a reactionchamber, in which at least the oxidation step is carried out. Duringoxidation of the nitride layer, the nitrogen present in the nitridelayer is replaced by oxygen.

After the oxidation step, the layer stack may contain nitrogen merely inplaces. Alternatively or additionally, the layer stack may belight-transmitting after oxidation. It is furthermore possible for thenitride layer to be completely oxidized in the oxidation step to yieldthe oxide layer. In particular, after the oxidation step, the oxidelayer may, within the bounds of manufacturing tolerances, be free ofnitrogen.

According to at least one embodiment of the method, application of theoxide layer comprises the following steps: providing a nitride layerwhich contains indium and at least partially oxidizing the nitride layerin an oxidation step to yield the oxide layer.

According to at least one embodiment of the method, the nitride layer isprovided by means of epitaxial deposition. In particular, the nitridelayer may be grown epitaxially on layers of the semiconductor device tobe produced which have been provided in preceding method steps.

In contrast with direct deposition of the oxide layer, it is notnecessary to provide oxygen for deposition of the nitride layer. Theoxygen required for oxidation may be provided solely in the oxidationstep. This may also proceed outside a chamber for epitaxial growth. Theoxidation step may in particular be necessary due to possible opacity ofthe nitride layer.

According to at least one embodiment of the method, the oxidation stepis carried out after application of the contact layer. The contact layeris thus firstly deposited onto the intermediate face of the layer stackand then the oxidation step is carried out. The nitride layer is thenoxidized through the contact layer. It is here possible for the contactlayer likewise to be partially oxidized.

According to at least one embodiment of the method, at least theoxidation step is carried out in a reaction chamber. It is possible forfurther method steps to be carried out in the reaction chamber. Thereaction chamber may in particular be the chamber used for epitaxialdeposition by means of MOVPE.

During the oxidation step, a reaction temperature in the reactionchamber amounts to at least 460° C., preferably at least 480° C. andparticularly preferably at least 500° C. The reaction temperaturefurthermore amounts to at most 720° C., preferably at most 700° C. andparticularly preferably at most 650° C. The nitride layer is thusheat-treated. It is furthermore possible for oxygen-containing gas, inparticular oxygen-containing gas, to be introduced into the reactionchamber during the oxidation step. Oxidation of the nitride layer isenabled by providing oxygen and simultaneously establishing the reactiontemperature.

According to at least one embodiment of the method, the oxide layer isapplied by means of epitaxial deposition of indium oxide. In particular,the oxide layer is grown epitaxially, for example, by means of MOVPE, onlayers of the semiconductor device to be produced which have beenprovided in preceding method steps. It is here in particular possiblefor the method not to comprise a separate oxidation step for oxidizing anitride layer

For example, the semiconductor layer sequence may firstly be grownepitaxially on the growth carrier. The semiconductor layer sequence is,for example, formed with In_(n)Ga_(1-n)N. By gradually reducing galliumand/or nitrogen and increasing the oxygen content in the reactionchamber, it is possible to change over to epitaxially growing indiumoxide or optionally indium nitride.

According to at least one embodiment of the method, the nitride layer isdeposited epitaxially under three-dimensional growth conditions. Theoxide layer may furthermore be deposited under three-dimensional growthconditions. It is also possible for the entire layer stack to bedeposited epitaxially under three-dimensional growth conditions.

Three-dimensional growth may be described by the Volmer-Weber growthmodel or by the Stranski-Krastanov growth model. Specific growthconditions, such as, for example, a reduction in reactor temperature, anincrease in reactor pressure and/or a reduction in the V/III ratio, arein particular necessary for three-dimensional growth. In the case ofthree-dimensional growth, the growth rate along the stack direction maybe increased in comparison with the growth rate along at least one ofthe lateral directions.

According to at least one embodiment of the method, the nitride layerhas a multiplicity of multilayer islands which are not joined together.It is alternatively possible for the oxide layer to be depositedepitaxially under three-dimensional growth conditions in such a mannerthat the oxide layer has multilayer islands which are not joinedtogether. In particular, the islands are not joined together in lateraldirections. In other words, the nitride layer and/or the oxide layeris/are not contiguous. In particular, the intermediate face may benon-contiguous. For example, the islands have a trapezoidal and/ortriangular cross-section along the stack direction. The islands may bepyramidal and/or truncated pyramidal. “Multilayer” means here andhereinafter that the islands contain a plurality of monolayers grown onone another. A “monolayer” should here and hereinafter be taken to meana continuous layer of atoms or molecules, wherein the layer heightamounts to just one atom or molecule. In particular, no identical atomsor molecules are located on top of one another in a monolayer.

Epitaxial deposition under three-dimensional growth conditions may inparticular result in incomplete coverage of the top face by the nitridelayer and thus by the oxide layer. In other words, in the regionsbetween the islands of the oxide layer, the top face is free of thenitride layer. The oxide layer or optionally the nitride layer may, forexample, be grown directly on the top face. In this case, in the regionsbetween the islands of the oxide layer or the nitride layer, the topface may be freely accessible directly after growth of the oxide layeror nitride layer.

According to at least one embodiment of the method, the nitride layer isdeposited epitaxially under three-dimensional growth conditions in sucha manner that the nitride layer has a multiplicity of multilayer islandswhich are not joined together.

It is furthermore possible for the oxide layer to be depositedepitaxially under three-dimensional growth conditions in such a mannerthat the oxide layer has a multiplicity of multilayer islands which arenot joined together.

According to at least one embodiment of the method, epitaxial depositionproceeds under two-dimensional growth conditions. In particular, theoxide layer or the nitride layer is epitaxially deposited undertwo-dimensional growth conditions. It is also possible for the entirelayer stack to be deposited epitaxially under two-dimensional growthconditions.

In two-dimensional growth, the atomic layers of the oxide layer aregrown monolayer by monolayer. For example, the two-dimensionally grownoxide layer and/or nitride layer comprises in the stack direction atleast one and at most three, preferably at most two, monolayers.Two-dimensional growth may, for example, be described by aFrank-van-der-Merve growth model or by the Stranski-Krastanov growthmodel. In two-dimensional growth, the growth rate along at least one ofthe lateral directions may be higher than or equally high as the growthrate along the stack direction.

According to at least one embodiment of the method, the oxide layer iscontiguous. In other words, the oxide layer is of one-piececonstruction. In particular, the intermediate face may be simplyconnected. In particular, the oxide layer may completely cover the topface. In other words, the top face is no longer freely accessible oncethe nitride layer or oxide layer has been deposited. It is furthermorepossible for the entire layer stack to be contiguous.

According to at least one embodiment of the method, epitaxial depositionproceeds under two-dimensional growth conditions in such a manner thatthe oxide layer is contiguous.

According to at least one embodiment of the method, the layer stackcomprises a first interlayer. The first interlayer is formed with indiumgallium oxide, preferably InGaO₃. The first interlayer may, within thebounds of manufacturing tolerances, consist of indium gallium oxide.

According to at least one embodiment of the method, a nitride interlayerwhich is formed with indium gallium nitride is initially epitaxiallydeposited for application of the first interlayer. The nitrideinterlayer may, for example, be directly epitaxially deposited onto thetop face. In particular, the nitride interlayer is deposited before thenitride layer is deposited. The nitride interlayer may thus be arrangedupstream from the nitride layer in the stack direction. The nitrideinterlayer layer is then at least partially oxidized in the oxidationstep to yield the first interlayer. In particular, the nitrideinterlayer is oxidized to yield the first interlayer in the same methodstep as the nitride layer is oxidized to yield the oxide layer. Afterthe oxidation step, the first interlayer is arranged between thesemiconductor layer sequence and the oxide layer. In particular, thefirst interlayer may directly adjoin the oxide layer.

Alternatively, the first interlayer may be provided by means ofepitaxial deposition of indium gallium oxide, in particular onto the topface.

According to at least one embodiment of the method, the contact layer isapplied onto the intermediate face under growth conditions in which, inthe event of direct application onto the top face, a (100) orientationof the crystal structure of the contact layer would be obtained andwherein the crystal structure of the contact layer has a (111) crystalorientation. The numbers between brackets here indicate the Millerindices of the lattice plane closest to the top face. In a (100) crystalorientation, the outer faces of the crystal are parallel to one of thecube faces of the structure cell. In a (111) crystal orientation, theouter faces of the crystal are located diagonally to the structure cellsthereof. It has here surprisingly been found that, despite selecting forgrowth conditions for a (100) crystal orientation, a (111) crystalorientation of the crystal structure of the contact layer is formed.Such a (111) crystal orientation is, for example, distinguished byparticularly good electrical contact to the underlying layers.

In an alternative semiconductor device, in which the contact layer isapplied directly onto the top face, growth conditions for (100) crystalorientation of the contact layer are selected, since here a betterconnection and/or a better crystal quality of the boundary regionbetween the contact layer and the top face are obtained.

An optoelectronic semiconductor device is furthermore provided. Theoptoelectronic semiconductor device can preferably be produced by meansof one of the methods described here. That is to say, all the featuresdisclosed for the method are also disclosed for the semiconductor deviceand vice versa.

According to at least one embodiment of the optoelectronic semiconductordevice, the latter comprises a semiconductor layer sequence with alight-emitting and/or light-absorbing active zone and with a top facewhich is downstream of the active zone in a stack direction extendingperpendicular to a main plane of extension of the semiconductor layersequence. The optoelectronic semiconductor device furthermore comprisesa layer stack applied to the top face with an oxide layer, whichcontains indium, and an intermediate face downstream of the top face inthe stack direction. The optoelectronic semiconductor device alsocomprises a contact layer, which is formed with indium tin oxide,applied to the intermediate face. The layer stack is, within the boundsof manufacturing tolerances, free of tin.

Verification that the layer stack is, within the bounds of manufacturingtolerances, free of tin can be obtained, for example, by means of EDXanalysis (EDX=energy-dispersive X-ray spectroscopy) on the completedsemiconductor device. Using EDX analysis, it is in particular possibleto investigate the elemental composition of the individual layers of theoptoelectronic semiconductor device. In particular, EDX analysis canprovide an EDX spectrum of the chemical elements in the semiconductordevice as a function of the position of the investigated layer along thestack direction. For example, starting from the top face of thesemiconductor layer sequence, the oxygen content in the EDX spectruminitially increases in the stack direction. From the intermediate face,the tin content in the EDX spectrum may, for example, increase.

For example, the oxide layer may have been produced by at least partialoxidation of a nitride layer. Such oxidation is, for example, detectableby the presence of nitrogen in the oxide layer. It is alternativelypossible for the oxide layer to have been produced by epitaxialdeposition of indium oxide. In the case of epitaxial deposition of theoxide layer, a continuous change in the crystal structure and/orchemical composition of the individual layers, in particular over aplurality of monolayers, is obtained in the stack direction. Atransitional zone in which the composition of the crystal changes isformed between the successively grown individual layers, in particularbetween the optionally present first interlayer and the oxide layer. Thetransitional zone may have a thickness of one to two monolayers in thestack direction. Use of an epitaxial deposition method can be detectedon the completed semiconductor device on the basis of the presence ofsuch a transitional zone.

According to at least one embodiment of the optoelectronic semiconductordevice, the oxide layer is, within the bounds of manufacturingtolerances, free of gallium. In other words, the oxide layer does notconsist of indium gallium oxide. Production-related gallium impuritiesmay here be present in the oxide layer. For example, the number ofgallium atoms in the oxide layer amounts to at most 1%, preferably atmost 0.5% and particularly preferably at most 0.1%, of the number ofindium atoms in the oxide layer. EDX analysis is likewise capable ofdetecting that the oxide layer is, within the bounds of manufacturingtolerances, free of gallium.

According to at least one embodiment of the optoelectronic semiconductordevice, the layer stack has a first interlayer which is formed withindium gallium oxide. The first interlayer is arranged between thesemiconductor layer sequence and the oxide layer. The first interlayerdirectly adjoins the oxide layer. The first interlayer may furthermoredirectly adjoin the top face of the semiconductor layer sequence.Alternatively, a second interlayer may be arranged between the firstinterlayer and the semiconductor layer sequence.

For example, the first interlayer may have been produced by at leastpartial oxidation of a nitride interlayer. Such oxidation is, forexample, detectable by the presence of nitrogen in the first interlayer.It is alternatively possible for the first interlayer to have beenproduced by epitaxial deposition of indium gallium oxide, for example,onto the top face. In particular, the epitaxial growth of thesemiconductor layers of the semiconductor layer sequence maycontinuously transition into the epitaxial growth of the firstinterlayer by the nitrogen used in growing the semiconductor layersequence being continuously replaced by oxygen.

According to at least one embodiment of the optoelectronic semiconductordevice, the layer stack comprises a second interlayer. The secondinterlayer is formed with indium gallium nitride. The second interlayermay, within the bounds of manufacturing tolerances, consist of indiumgallium nitride. The second interlayer is arranged between thesemiconductor layer sequence and the first interlayer. The secondinterlayer furthermore directly adjoins the top face. The secondinterlayer is, within the bounds of manufacturing tolerances, free ofoxygen.

It is in particular possible for the layer stack exclusively to consistof the first interlayer, the second interlayer and the oxide layer. Inparticular, the layer stack may comprise, in the stack direction,firstly the second interlayer, then the first interlayer andsubsequently the oxide layer.

According to at least one embodiment of the optoelectronic semiconductordevice, the layer stack includes indium nitride. A production method forthe oxide layer can be detected on the completed semiconductor device onthe basis of such presence of indium nitride. It is accordingly inparticular possible for the oxide layer to have been produced bydeposition of a nitride layer and subsequent oxidation of the nitridelayer in the oxidation step. In the event of incomplete oxidation of thenitride layer, residues of indium nitride remain present in the layerstack. These residues may be detected, for example, using EDX analysis,by means of X-ray diffraction (XRD) and/or by means of spectroscopy.

According to at least one embodiment of the optoelectronic semiconductordevice, the crystal structure of the contact layer has a (iii) crystalorientation. The crystal structure of the contact layer may, forexample, be determined using X-ray methods and/or electron microscopydiffraction methods.

According to at least one embodiment of the optoelectronic semiconductordevice, the oxide layer has a multiplicity of multilayer islands whichare not joined together. In other words, the oxide layer has been grownby means of three-dimensional growth. The extent of the islands inlateral directions may in particular amount to at most the wavelength ofthe light emitted and/or absorbed by the active zone. The islands, forexample, serve as outcoupling structures for the light emitted in thedirection of the oxide layer by the active zone. Alternatively oradditionally, the islands may serve as injection structures for thelight incident from the direction of the oxide layer and absorbed by theactive zone. Outcoupling or injection structures may here andhereinafter be structures which improve the transmission of the emittedand/or absorbed light at the interface between the islands and thelayers directly adjoining the islands in the stack direction. Inparticular, the islands may to this end have an average extent in thelateral directions which at most corresponds to the wavelength of thelight. In other words, reflection of the light impinging on saidinterface is reduced.

According to at least one embodiment of the optoelectronic semiconductordevice, the oxide layer is contiguous. In other words, the oxide layerhas no holes and/or recesses. In particular, the oxide layer is ofone-piece construction. A contiguous oxide layer may have been grownunder two-dimensional growth conditions.

According to at least one embodiment of the optoelectronic semiconductordevice, the average thickness of the oxide layer along the stackdirection amounts to at least 0.5 and at most three monolayers. Theaverage thickness of the oxide layer is here the mathematically averagedthickness. It is accordingly in particular possible for the oxide layerto have regions in which the oxide layer locally has a thickness whichamounts to more than three monolayers or less than 0.5 monolayers.

According to at least one embodiment of the optoelectronic semiconductordevice, the average height of the islands along the stack directionamounts to at least 50, preferably at least 100, and at most 200,preferably at most 160, monolayers. In particular, the average height ofthe islands may amount to at least 25 nm, preferably at least 50 nm, andat most 100 nm, preferably at most 80 nm. The height of the islands ishere defined by the number of monolayers in an island. The averageheight of the islands is the number of monolayers of all the islandsaveraged over the number of islands. It is accordingly in particularpossible for at least one of the islands to have a number of less than50, preferably less than 100, or more than 200, preferably more than160, monolayers.

According to at least one embodiment of the optoelectronic semiconductordevice, a first boundary region between the semiconductor layer sequenceand the layer stack and/or a second boundary region between the layerstack and the contact layer have a lower density of defects than analternative boundary region between a semiconductor layer sequence and acontact layer of an alternative semiconductor device, in which thecontact layer is applied directly onto the semiconductor layer. Inparticular, the alternative boundary region may have a higher number ofcontaminants, defects and/or instances of damage than the first and/orsecond boundary region.

In the alternative boundary region, deposition of the contact layer ontothe semiconductor layer sequence results in damage to the top face ofthe semiconductor layer sequence. In particular, the contact layer andthe semiconductor layer sequence are formed with extremely differentmaterials, whereby production-related contaminants and/or defects areformed. Introducing the layer stack between the semiconductor layersequence and the contact layer permits gradual adaptation of the crystalstructure and/or materials.

BRIEF DESCRIPTION OF THE DRAWINGS

The method described here and the optoelectronic semiconductor devicedescribed here are explained in greater detail below with reference toexemplary embodiments and the associated figures.

FIG. 1 shows an exemplary embodiment of a semiconductor device describedhere.

FIG. 2 shows a method step of an exemplary embodiment of a methoddescribed here.

FIG. 3 shows an alternative optoelectronic semiconductor device.

FIG. 4 shows an exemplary embodiment of a semiconductor device describedhere.

FIG. 5 shows an exemplary embodiment of an optoelectronic semiconductordevice described here and of a method described here.

FIG. 6 shows the work function of the materials used as a function ofthe energy band gap.

FIG. 7 shows X-ray diffraction spectra of an optoelectronicsemiconductor device described here.

FIG. 8 shows a sketched EDX signal of an optoelectronic semiconductordevice described here.

Identical, similar or identically acting elements are provided with thesame reference numerals in the figures. The figures and the size ratiosof the elements illustrated in the figures relative to one another arenot to be regarded as being to scale. Rather, individual elements may beillustrated on an exaggeratedly large scale for greater ease ofdepiction and/or better comprehension.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

An exemplary embodiment of an optoelectronic semiconductor devicedescribed here is explained in greater detail with reference to theschematic sectional representation of FIG. 1. The semiconductor devicecomprises a semiconductor layer sequence 1, a layer stack 2 and acontact layer 3.

The semiconductor layer sequence 1 extends along a main plane ofextension. The stack direction z extends perpendicular to the main planeof extension.

The semiconductor layer sequence 1 successively comprises in the stackdirection a first semiconductor layer 11, an active zone 12, a secondsemiconductor layer 13 and a highly doped semiconductor layer 14. Thefirst semiconductor layer 11 may, for example, be an n-conductivesemiconductor layer. The second semiconductor layer 13 may bep-conductive. The active zone 12 is provided for emitting and/ordetecting light. An outer face of the highly doped semiconductor layer14 forms the top face 1 a of the semiconductor layer sequence 1. The topface 1 a succeeds the active zone 12 of the semiconductor layer sequence1 in the stack direction z.

The highly doped semiconductor layer 14 may be p-conductive and be dopedwith magnesium. The highly doped semiconductor layer 14 may, forexample, have been activated in a method step with oxygen, in particularusing an oxygen-containing gas. To this end, subsequent to epitaxialdeposition of the highly doped semiconductor layer 14 in the reactionchamber, the temperature in the reaction chamber may be reduced toapprox. 615° C. With addition of an oxygen-containing gas, thep-conductive material of the highly doped semiconductor layer may beactivated in a further process step.

The layer stack 2 is applied onto the top face 1 a. Layer stack 2comprises a second interlayer 22, a first interlayer 21 and an oxidelayer 20. The second interlayer 22 is applied to the top face 1 a of thesemiconductor layer sequence 1. The second interlayer 22 may, forexample, be formed with indium gallium nitride. The first interlayer 21may, for example, be formed with indium gallium oxide. The oxide layer20 may furthermore be formed with or consist of indium oxide. An outerface of the oxide layer 20 remote from the semiconductor layer sequence1 forms an intermediate face 2 a of the layer stack 2.

Unlike the representation in FIG. 1, it is possible for no secondinterlayer 22 to be present and for the first interlayer 21 to beapplied directly onto the top face 1 a. It is also possible for thelayer stack 2 exclusively to comprise the oxide layer 20.

The contact layer 3 is applied to the intermediate face 2 a. The contactlayer 3 is, for example, formed with indium tin oxide. In particular,the contact layer 3 is light-transmitting. An outer face of the contactlayer 3 forms a light passage face 3 a of the optoelectronicsemiconductor device.

A first boundary region 32 is arranged between the semiconductor layersequence 1 and the layer stack 2 and a second boundary region 33 isarranged between the layer stack 2 and the contact layer 3. The firstboundary region 32 and/or the second boundary region 33 have a lowerdefect density than an alternative boundary region 31 (not shown inFIG. 1) in which the contact layer 3 is applied directly to the top face1 a.

A method step of a method described here for producing an optoelectronicsemiconductor device is explained in greater detail on the basis of theschematic sectional representation of FIG. 2. In the method step shown,a nitride interlayer 202 is applied onto the top face is and, followingon in the stack direction, a nitride layer 201 is applied onto thenitride interlayer 202. It is however alternatively also possible,unlike in FIG. 2, for no nitride interlayer 202 to be present.

The nitride interlayer 202 and the nitride layer 201 contain a nitride.The nitride interlayer 202 may be formed with indium gallium nitride.The nitride layer 202 may be formed with indium nitride.

In the method step illustrated, oxygen-containing gas 51 is provided. Bymeans of the oxygen-containing gas 51, the nitride layer 201 is oxidizedto yield the oxide layer 20. It is here possible for the nitride layer201 merely to be partially oxidized to yield the oxide layer 20. It isfurthermore possible for the nitride layer 201 to be completely oxidizedto yield the oxide layer 20.

The nitride interlayer 202 may also be oxidized to yield the firstinterlayer 21. It is furthermore possible for the nitride interlayer 202to be only partially oxidized. In particular, part of the nitrideinterlayer 202 may be oxidized to yield the first interlayer 21, while afurther part of the nitride interlayer 202 is not oxidized and forms thesecond interlayer 22.

FIG. 3 shows an alternative semiconductor device with reference to aschematic sectional representation. The alternative semiconductor devicecomprises a semiconductor layer sequence 1, which has the same structureas the semiconductor layer sequence 1 of the optoelectronicsemiconductor device of FIG. 1. The contact layer 3 is applied onto thetop face 1 a of the semiconductor layer sequence 1. As a result, analternative boundary region 31 between the semiconductor layer sequence1 and the contact layer 3 is obtained. Due to the absence of the layerstack 2 between the semiconductor layer sequence 1 and the contact layer3, the alternative boundary region 31 has a higher number of defects,contaminants and/or instances of damage. The contact layer 3 of thealternative semiconductor device may, for example, be deposited by meansof a gentle deposition method, such as, for example, vapor deposition,in order to minimize damage within the alternative boundary region. Thecontact layer 3 may alternatively or additionally be applied by means ofsputtering.

A further exemplary embodiment of an optoelectronic semiconductor devicedescribed here is explained in greater detail with reference to theschematic sectional representation of FIG. 4. In contrast with theexemplary embodiment of FIG. 1, a region of the first semiconductorlayer 11 is uncovered, in which a further top face 1 a′ of thesemiconductor layer sequence is formed. A further contact layer 3′ isapplied to the further top face 1 a′. The further contact layer 3′ hasthe same structure, in particular the same crystal orientation, as thecontact layer 3. It is in particular possible for both the contact layer3 and the further contact layer 3′ to have a (111) crystal orientationof the crystal structure. A contact 4, which is in direct contact withthe further contact layer 3′, is arranged on the further contact layer3′. The contact 4 may be formed with a metal, such as, for example,platinum.

A further exemplary embodiment of a semiconductor device described hereand a method described here will be explained in greater detail withreference to the perspective sectional representation in FIG. 5. Thelayer stack 2 is applied to the top face is of the semiconductor layersequence 1. The layer stack 2 has in the present case been grown usingthree-dimensional growth conditions. As a result, the layer stack 2 issubdivided into islands 200. The islands 200 are arranged spaced fromone another on the top face 1 a. In particular, the islands 200 are notjoined together in lateral directions. The islands 200 have atrapezoidal and/or triangular cross-section.

The contact layer 3 is applied onto the interlayer 2 a and the regionsof the top face is not covered by the layer stack 2 or the oxide layer20. The shape of the contact layer 3 follows the shape of the layerstack 2. In particular, the radiation passage face 3 a is in each caseat a uniform distance from the underlying layers. In other words, thecontact layer 3 is a conformal layer and, within the bounds ofmanufacturing tolerances, has a uniform thickness.

FIG. 6 explains in greater detail a mode of operation of theoptoelectronic semiconductor device described here on the basis of thework function W as function of the energy band gap E_(B). The secondsemiconductor layer 13 and/or the highly doped semiconductor layer 14is, for example, formed with p-conductive gallium nitride which has awork function of about 7.5 eV. A material which likewise has a high workfunction is desirable for electrically contacting the highly dopedsemiconductor layer 14 and/or the second semiconductor layer 13.Platinum (work function: 5.65 eV) or nickel (work function: 5.15 eV)are, for example, suitable for this purpose. Platinum and nickel are,however, opaque and are thus unsuitable as a front surface contact of asemiconductor device. Gallium indium oxide likewise has a high workfunction of 5.4 eV. In contrast with gallium indium oxide, indium tinoxide (work function: 4.7 to 4.8 eV) is, however, a well known material.Gallium indium oxide furthermore has higher absorption for the lightgenerated in the active zone.

On the basis of X-ray diffraction spectra (XRD), FIG. 7 explains ingreater detail a mode of operation of a method described here. Signalintensity I in counts per second (cps) is shown as a function of twicethe angle of reflection on the plane 2θ in degrees. A spectrum before anoxidation step 71, a spectrum after the oxidation step 72 and acomparison spectrum 73, in which no oxidation was carried out, are shownhere.

The spectrum before oxidation 71 has a first maximum 701 and a secondmaximum 703. The first maximum 701 corresponds to the indium nitridepresent in the nitride layer 201. The second maximum 703 corresponds tothe gallium nitride present in the semiconductor layer sequence 1.

The spectrum after oxidation 72 has a second maximum 702. The secondmaximum 702 corresponds to the indium oxide produced by oxidation of theoxide layer 20. In addition, the first maximum 701 at indium nitride isno longer apparent. The indium nitride has been oxidized to yield indiumoxide. The third maximum 703 is unchanged within the bounds of measuringaccuracy. The material of semiconductor layer sequence 1 has thus notbeen oxidized and/or changed by the oxidation.

The comparison spectrum 73 shows the X-ray diffraction spectrum of analternative semiconductor device. The comparison spectrum 73 only has,within the bounds of measuring accuracy, the third maximum 703.

An optoelectronic semiconductor device described here is explained ingreater detail on the basis of the sketched EDX spectrum of FIG. 8. Anormalized EDX signal S is plotted as a function of position in thestack direction z. An oxide content 81 increases in the region of thetop face 1 a. A tin content 82 increases in the region of theintermediate face 2 a. The rising flanks of the EDX signals for oxidecontent 81 and tin content 72 are offset from one another in the stackdirection z. On the basis of these different positions of the risingflanks, it is possible to detect the presence of the layer stack 2between the semiconductor layer sequence 1 and the contact layer 3 inthe completed semiconductor device.

The description made with reference to exemplary embodiments does notrestrict the invention to these embodiments. Rather, the inventionencompasses any novel feature and any combination of features, includingin particular any combination of features in the claims, even if thisfeature or this combination is not itself explicitly indicated in theclaims or exemplary embodiments.

1-20. (canceled)
 21. A method for producing an optoelectronicsemiconductor device, the method comprising: providing a semiconductorlayer sequence comprising a light-emitting and/or light-absorbing activezone and a top face downstream of the active zone in a stack directionextending perpendicular to a main plane of extension of thesemiconductor layer sequence; applying a layer stack onto the top face,wherein the layer stack comprises an oxide layer containing indium, andan intermediate face downstream of the top face in the stack direction;and applying a contact layer onto the intermediate face, wherein thecontact layer comprises indium tin oxide, and wherein the layer stackis, within the bounds of manufacturing tolerances, free of tin.
 22. Themethod according to claim 21, wherein applying the oxide layer comprisesproviding a nitride layer containing indium, and at least partiallyoxidizing the nitride layer to form the oxide layer.
 23. The methodaccording to claim 22, wherein oxidizing is performed after applying thecontact layer.
 24. The method according to claim 22, wherein the nitridelayer is epitaxially deposited under three-dimensional growth conditionssuch that the nitride layer has a plurality of multilayer islands whichare not joined together.
 25. The method according to claim 21, whereinat least oxidizing is performed in a reaction chamber and, whileoxidizing, a reaction temperature in the reaction chamber amounts to atleast 460° C. and at most 720° C.
 26. The method according to claim 21,wherein applying the oxide layer comprises epitaxial depositing indiumoxide.
 27. The method according to claim 26, wherein epitaxialdepositing comprises epitaxial depositing under two-dimensional growthconditions such that the oxide layer is contiguous.
 28. The methodaccording to claim 21, wherein the layer stack comprises a firstinterlayer formed with indium gallium oxide, and wherein applying thefirst interlayer comprises epitaxially depositing a nitride interlayer,formed with indium gallium nitride, and at least partial oxidizing thenitride interlayer to form the first interlayer.
 29. The methodaccording to claim 21, wherein the contact layer is applied onto theintermediate face under growth conditions in which, in the case ofdirect application onto the top face, a crystal orientation of a crystalstructure of the contact layer is obtained, and wherein the crystalstructure of the contact layer has a crystal orientation.
 30. Aoptoelectronic semiconductor device comprising: a semiconductor layersequence including a light-emitting and/or light-absorbing active zoneand a top face downstream of the active zone in a stack directionextending perpendicular to a main plane of extension of thesemiconductor layer sequence; a layer stack arranged at the top face,the layer stack including an oxide layer containing indium, and anintermediate face downstream of the top face in the stack direction; anda contact layer arranged at the intermediate face, the contact layercomprising indium tin oxide, wherein the layer stack is, within thebounds of manufacturing tolerances, free of tin.
 31. The optoelectronicsemiconductor device according to claim 30, wherein the oxide layer is,within the bounds of manufacturing tolerances, free of gallium.
 32. Theoptoelectronic semiconductor device according to claim 30, wherein thelayer stack further includes a first interlayer comprising indiumgallium oxide, wherein the first interlayer is arranged between thesemiconductor layer sequence and the oxide layer and directly adjoinsthe oxide layer.
 33. The optoelectronic semiconductor device accordingto claim 32, wherein the layer stack further includes a secondinterlayer comprising indium gallium nitride, wherein the secondinterlayer is arranged between the semiconductor layer sequence and thefirst interlayer and directly adjoins the top face, and wherein thesecond interlayer is, within the bounds of manufacturing tolerances,free of oxygen.
 34. The optoelectronic semiconductor device according toclaim 30, wherein the layer stack includes indium nitride.
 35. Theoptoelectronic semiconductor device according to claim 30, wherein acrystal structure of the contact layer has a crystal orientation. 36.The optoelectronic semiconductor device according to claim 30, whereinthe oxide layer has a plurality of multilayer islands which are notjoined together.
 37. The optoelectronic semiconductor device accordingto claim 36, wherein an average height of the islands along the stackdirection amounts to at least 50 and at most 200 monolayers.
 38. Theoptoelectronic semiconductor device according to claim 30, wherein theoxide layer is contiguous.
 39. The optoelectronic semiconductor deviceaccording to claim 30, wherein an average thickness of the oxide layeralong the stack direction amounts to at least 0.5 and at most 3monolayers.
 40. The optoelectronic semiconductor device according toclaim 30, wherein a first boundary region between the semiconductorlayer sequence and the layer stack and/or a second boundary regionbetween the layer stack and the contact layer have a lower density ofdefects than an alternative boundary region between a semiconductorlayer sequence and a contact layer of an alternative semiconductordevice, in which the contact layer is applied directly onto thesemiconductor layer sequence.
 41. A method for producing a semiconductordevice, the method comprising: providing a semiconductor layer sequenceincluding an active zone and a top face downstream of the active zone ina stack direction extending perpendicular to a main plane of extensionof the semiconductor layer sequence; applying a layer stack onto the topface, wherein the layer stack comprises an oxide layer containingindium, and an intermediate face downstream of the top face in the stackdirection, wherein a nitride layer containing indium is provided and thenitride layer is at least partially oxidized to form the oxide layer;and applying a contact layer onto the intermediate face, the contactlayer comprising indium tin oxide, wherein the layer stack is, withinthe bounds of manufacturing tolerances, free of tin.